1. Field of the Invention
The present invention relates to an electro luminescence device, and more particularly to an electro luminescence device including a light shield element formed on side surfaces of its luminescence layer and adapted to shield light emitted in a direction toward the side surfaces of luminescence layer, thereby capable of obtaining improvements in luminance and contrast for each pixel thereof, and a method for fabricating the same.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated a conventional electro luminescence device. As shown in FIG. 1, the conventional electro luminescence device includes a substrate 1 and a lower electrode 2 formed on the substrate 1. Sequentially formed on the lower electrode 2 are a first insulation film 3, a luminescence layer 4 and a second insulation film 5. An upper electrode 6 is formed on the second insulation film 5.
Now, fabrication of the electro luminescence device having the above-mentioned structure will be described.
First, an indium tin oxide (ITO) layer is deposited over the substrate 1 comprised of, for example, a glass substrate. Over the ITO layer, a photoresist film is then coated. The photoresist film is then subjected to a patterning to form a predetermined pattern. Using the patterned photoresist film as a mask, the ITO layer is etched, thereby forming the lower electrode 2 made of ITO.
Thereafter, formation of the first insulation film 3 is carried out by depositing an insulation material such as Ta.sub.2 O.sub.5 or SiO.sub.2 over the lower electrode by use of a sputtering process.
The first insulation film 3 should exhibit a high dielectric constant, a high dielectric breakdown strength, a superior transmittance and a superior adhesiveness.
The luminescence layer 4 is then deposited over the first insulation film 3 using an electron-beam evaporation process or the sputtering process. As the luminescence layer 4, a layer of a Group II-VI semiconductor is mainly used. As such a layer, a Mn-doped ZnS layer is used in this case.
Accordingly, the luminescence layer 4 has a spectrum of the visible light range and a wide energy band gap and exhibits matched charge compensation and ion radius between the luminous basic body of ZnS and the luminous center body of Mn.sup.2+.
Subsequently, the second insulation film 5 is deposited over the luminescence layer 4 using the sputtering process. Using the electron-beam evaporation process, an aluminum layer is then deposited over the second insulation film 5. In this case, the second insulation film 5 may be made of the same material as the first insulation film 3 or made of a material different from the first insulation film 3.
Then, a photoresist film is coated over the aluminum layer. The photoresist film is then subjected to a patterning to form a predetermined pattern. Using the patterned photoresist pattern as a mask, the aluminum layer is etched, thereby forming the upper electrode 6 comprised of the aluminum layer.
Thereafter, a photoresist film not shown is coated over the resulting structure and then subjected to a patterning to form a predetermined pattern, using a well-known photo-etching process. Using the patterned photoresist pattern not shown as a mask, the second insulation film 5, the luminescence layer 4 and the first insulation film 3 are sequentially etched so that a pad portion of the lower electrode 2 can be exposed.
In this case, the etching process used is the reactive ion etch (RIE) process which is a kind of dry etching process.
Operation of the conventional electro luminescence device fabricated in accordance with the above-mentioned method will now be described, in conjunction with FIG. 2.
As an AC voltage is applied between the lower electrode 2 and the upper electrode 6, charges being present at the interface between the first insulation film 3 and the luminescence layer 4 and the interface between the luminescence layer 4 and the second insulation film 5 tunnel into the conduction band of the luminescence layer 4. During the tunneling, the charges are accelerated by a high electric field generated in the luminescence layer 4, thereby generating hot electrons.
These accelerated hot electrons impact against the luminous center bodies of Mn.sup.2+ doped in the luminous basic bodies of Zns of the luminescence layer 4, thereby ionizing the luminous center bodies. As the luminous center bodies ionize, they are excited. A part of hot electrons ionize the luminous bodies, so that they are coupled with holes. As a result, electron-hole pairs are formed.
On the other hand, the electrons excited up to the conduction band of the luminescence layer 4 fall down to the valence band of the luminescence layer 4. As a result, light is emitted from the luminescence layer 4. The emitted light has an energy corresponding to the energy difference between the conduction band and the valence band of the luminescence layer 4.
In the conventional electro luminescence device, only about 1/10 of the total light amount emitted from the luminescence layer 4 is emitted in a direction toward the lower electrode 2 which is the part used as a display element. The remaining part, namely, about 9/10 of the total light is emitted in directions other than in a direction toward the lower electrode 2. This will be described in detail.
As shown in FIG. 3, the luminescence layer 4 emits a larger amount of light toward side surfaces of a corresponding pixel than that emitted toward the upper surface of the lower electrode 2. As a result, where the light emitted from the luminescence layer 4 is a blue color light, this blue color light exhibits too low luminance to be practically employed in display elements.
Since the light from the luminescence layer 4 is emitted in a large amount in directions other than in direction toward the upper electrode 6, namely, toward a viewer, it affects other neighboring pixels. As a result, each pixel exhibits a degradation in contrast.